The present invention relates to grease compositions which contain a functionalized polymer which serves as a thickener or rheology modifier.
Greases typically comprise a base oil and a thickener, which is normally an acid-containing material. In some instances polymers also have been added to grease compositions in an attempt to improve performance characteristics such as dropping points, cone penetration, water wash-off, or oil separation.
U.S. Pat. No. 3,591,499, Morway, Jul. 6, 1971, discloses a grease containing a metal salt of an .alpha.,.omega.-dicarboxylic acid of molecular weight 500-2500. The metal can be an alkali metal or alkaline earth metal. The salts of the branched carboxy-terminated dicarboxylic acids are more shear stable than is polyisobutylene, yet are still capable of imparting adhesiveness and stringiness to a grease. At the same time, these salts per se are capable of thickening oil to a grease structure.
U.S. Pat. No. 3,476,532, Hartman, Nov. 4, 1969, discloses metal-containing complexes of oxidized polyethylene, containing functional oxygen groups e.g. carbonyl, carboxyl, hydroxy, etc. The material is useful in production of grease-like compositions. The composition is a mixture of the oxidized poly-ethylene and a complexing agent selected from metal salts, metal salts of fatty acids, the metals being at least divalent, and metal complexes.
U.S. Pat. No. 4,877,557, Kaneshige et al., Oct. 31, 1989, discloses a lubricating oil composition comprising a synthetic hydrocarbon lubricating oil, a load withstanding additive, and a liquid modified ethylene/.alpha.-olefin random copolymer. The load withstanding additive is roughly divided into an oiliness agent and an extreme pressure agent. The oiliness agent can be higher fatty acids such as oleic acid and stearic acid. Extreme pressure agents include, for example, organic metal type extreme pressure agents. The load-withstanding additives can be used singly or in the form of a mixture of two or more of them. The liquid copolymer is prepared from an unmodified polymer with a number average molecular weight of 300 to 12,000.
Australian application 500,927, published in 1978 or 1979, discloses a lubricating grease comprising a paraffinic mineral oil, a calcium complex soap thickener, and an organic terpolymer of 65% ethylene, 5% ester comonomer, and 0.01-3% acid comonomer, melt index 0.5 to 200.
U.S. Pat. No. 5,275,747, Gutierrez et al., Jan. 4, 1994, discloses a derivatized ethylene alpha olefin polymer useful as a multifunctional viscosity index improver additive for oleaginous compositions. The alpha-olefin polymer is terminally unsaturated and has a number average molecular weight of above 20,000 to about 500,000. It is substituted with mono-or dicarboxylic acid-producing moieties; it can be reacted with metals to form salts. The additive has multifunctional viscosity index improver properties and can be used by incorporation and dissolution into an oleaginous material such as lubricating oils. Other additives may also be present; crankcase compositions can contain 2 to 8000 parts per million of calcium or magnesium, generally present as basic or neutral detergents.
In the present invention an acid-functionalized polymer is incorporated into a grease composition to provide thickening and improve the performance of the composition.